Method for measuring vertical acceleration and velocity of semi-active suspension system

ABSTRACT

The present invention relates to a method for measuring a vertical acceleration and a velocity of a semi-active suspension system. Particularly, the present invention provides a method for obtaining a vertical acceleration from vertical accelerations measured from three vertical acceleration sensors of a semi-active suspension system of a vehicle, comprising the steps of: receiving first to third vertical accelerations measured from first to third vertical acceleration sensors; and obtaining a fourth vertical acceleration (Ad) by multiplying the first to third vertical accelerations by correction constants and subsequently summing up them. Therefore, according to the present invention, a fourth vertical acceleration can be obtained by multiplying the three vertical accelerations measured from the three acceleration sensors by the constants for correcting them to accelerations at actually desired damper positions and subsequently summing up them, thereby enabling accurate measurement and correction of the vertical accelerations.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a semi-active suspension system of avehicle, and more particularly, to a method for measuring a verticalacceleration of a semi-active suspension system.

2. Description of the Prior Art

In general, a semi-active suspension system is an apparatus forimproving the driving stability and ride comfort of a vehicle bychanging the dynamic characteristics of dampers mounted in a vehicle inreal time. When a driver excessively steers a vehicle or the movement ofthe vehicle is out of its path, load unbalance of the vehicle causes thevehicle to be biased or not to be steerable so that the driver may be inunpredictable danger such as vehicle overturn. However, when a vehicle,which is mounted with the semi-active suspension system, drives on anuneven road, a vertical load at a contact surface of a tire and the roadis kept at an appropriate level, so that the stability of the vehiclecan be secured in steering, braking and driving. In addition, irregularshocks generated from the road when the vehicle travels are effectivelyabsorbed, so that the ride comfort and driving convenience can beprovided to a passenger and a driver.

Such a semi-active suspension system controls actuators and dampersrespectively connected to four road wheels after detecting the drivingconditions of the vehicle through vertical acceleration sensors, vehiclevelocity sensors, a steering angle sensor, a brake sensor, a throttleposition sensor, and the like among a variety of sensors mounted to thevehicle.

Among them, the vertical acceleration sensors are installed adjacent tofour dampers. However, since there is a difference between the practicalmounting positions of the acceleration sensors and the installationpositions of the dampers, it is difficult to accurately measure theaccelerations of the road wheels.

In a prior art, three vertical accelerations are measured through twovertical acceleration sensors mounted in front of a vehicle body and avertical acceleration sensor mounted at the rear thereof in the vicinityof the respective dampers, and a fourth vertical acceleration isobtained in such a manner that an ECU receives the three verticalaccelerations and calculates the other vertical acceleration usingEquation 1 as follows: $\begin{matrix}{{a_{RL} = {a_{RR} + {\frac{t_{R}}{t_{F}} \cdot \left( {a_{FL} - a_{FR}} \right)}}},} & (1)\end{matrix}$where a_(FL) is a vertical acceleration of a front left side, a_(FR) isa vertical acceleration of a front right side, a_(RL) is a verticalacceleration of a rear left side, a_(RR) is a vertical acceleration of arear right side, t_(F) is a front tread, and t_(R) is a rear tread.

Since it is difficult to accurately obtain a fourth verticalacceleration through calculation using the three vertical accelerationsand the threads of the road wheels, there is a problem with accuratedetermination of the dynamic characteristics of the vehicle.

Further, in the prior art, there is also a problem in that it isdifficult to accurately obtain a velocity even upon calculation thereoffrom three velocity sensors.

SUMMARY OF THE INVENTION

Accordingly, the present invention is conceived to solve theaforementioned problems in the prior art. An object of the presentinvention is to provide a method for measuring vertical accelerations ofa semi-active suspension system capable of accurately measuring andcorrecting the vertical accelerations in such a manner that verticalaccelerations measured from three acceleration sensors are multiplied byconstants for correcting them to accelerations at actually desiredpositions and are then summed up so as to obtain a fourth verticalacceleration.

Another object of the present invention is to provide a method formeasuring velocities of a semi-active suspension system capable ofaccurately measuring and correcting the velocities in such a manner thatthree velocities measured from three velocity sensors are multiplied byconstants for correcting them to velocities at actually desiredpositions and are then summed up so as to obtain a fourth velocity.

According to an aspect of the present invention for achieving theobjects, there is provided a method for obtaining a verticalacceleration from vertical accelerations measured from three verticalacceleration sensors of a semi-active suspension system of a vehicle,comprising the steps of receiving first to third vertical accelerationsmeasured from first to third vertical acceleration sensors; andobtaining a fourth vertical acceleration (Ad) by multiplying the firstto third vertical accelerations by correction constants and subsequentlysumming up them, according to the following equation:Ad=α×Aα1+β×Aα2+γ×Aα3,where α, β and γ are the correction constants at the position of adamper where a vertical acceleration sensor is not installed, Ad is thefourth vertical acceleration, and Aa1, Aa2 and Aa3 are the first tothird vertical accelerations, respectively.

According to another aspect of the present invention, there is provideda method for obtaining a velocity from velocities measured from threevelocity sensors of a semi-active suspension system of a vehicle,comprising the steps of receiving first to third velocities measuredfrom first to third velocity sensors; and obtaining a fourth velocity(Vd) by multiplying the first to third velocities by correctionconstants and subsequently summing up them, according to the followingequation:Vd=α×Vα1+βV×α2+γ×Vα3,where α, β and γ are the correction constants at the position of adamper where a velocity sensor is not installed, Vd is the fourthvelocity, and Va1, Va2 and Va3 are the first to third velocities,respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description ofpreferred embodiments given in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view showing positions of four dampers and three verticalacceleration sensors of a vehicle employing a semi-active suspensionsystem;

FIG. 2 is a block diagram of the semi-active suspension system,illustrating a method for measuring a vertical acceleration according tothe present invention;

FIG. 3 is a view showing positions of the four dampers and threevelocity sensors of the vehicle employing the semi-active suspensionsystem; and

FIG. 4 is a block diagram of a semi-active suspension system,illustrating a method for measuring a velocity according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a view showing positions of four dampers and three verticalacceleration sensors of a vehicle employing a semi-active suspensionsystem. Referring to this figure, two vertical acceleration sensors 10and 12 are mounted adjacent to front dampers 18 and 20 on a vehicle body1, respectively, while a vertical acceleration sensor 14 is mountedadjacent to one of rear dampers 22 and 24. Here, when “X” designates awidth direction of the vehicle body and “Y” designates a longitudinaldirection thereof, the positions of the two front vertical accelerationsensors 10 and 12 are indicated by coordinates (X₂, Y₂) and (X₁, Y₁),respectively, and the position of the rear vertical acceleration sensor14 is indicated by coordinates (X₃, Y₃). Reference numerals 1=FR, 2=FL,3=RR, and 4=RL, which have not yet been explained, designate thepositions of the first damper 18 at the front left side, the seconddamper 20 at the front right side, the third damper 22 at the rear leftside, and the fourth damper 24 at the rear right side, respectively.

In the present invention, correction constants for a verticalacceleration to be measured at a position where a fourth verticalacceleration sensor would be installed are obtained using the X and Yposition coordinate values (for example, X₁-X₂ and Y₁-Y₃) of the threevertical acceleration sensors 10, 12 and 14.

FIG. 2 is a block diagram of the semi-active suspension system,illustrating a method for measuring a vertical acceleration according tothe present invention. Referring to this figure, the semi-activesuspension system comprises the first to third vertical accelerationsensors 10, 12 and 14, an ECU 16, the first to fourth dampers 18, 20, 22and 24, and first to fourth actuators 26, 28, 30 and 32.

Each of the first to third vertical acceleration sensors 10, 12 and 14,which are installed adjacent to three of the four dampers of the vehiclebody, is a sensor for measuring a bounce motion of the vehicle andoutputting a vertical acceleration corresponding to the bounce motion ofthe vehicle body, as a voltage on a gravitational acceleration basis.

A microprocessor is used for the ECU 16, and the ECU includes controlalgorithms for bounce, roll, dive, squat and the like based on sky-hooklogic for independently controlling damping forces of the dampers ofrespective road wheels.

The first to fourth dampers 18, 20, 22 and 24 are equipped with variablevalves at lateral sides thereof so as to adjust the damping forces foruse in controlling the first to fourth actuators 26, 28, 30 and 32 whenthe dampers are extended and retracted.

In the semi-active suspension system configured as above, the method formeasuring the vertical acceleration according to the present inventionis performed as follows.

Vertical accelerations Aa1, Aa2 and Aa3 measured by the respective firstto third vertical acceleration sensors 10, 12 and 14 are input into theECU 16.

The ECU 16 receives the vertical accelerations Aa1, Aa2 and Aa3 measuredby the respective first to third vertical acceleration sensors 10, 12and 14 and obtains a fourth vertical acceleration Ad using Equation 2 asfollows:Ad=α×Aα1+β×Aα2+γ×Aα3,  (2)where α, β and γ are correction constants for the position of the fourthdamper where a fourth vertical acceleration sensor is not installed . Adis the the fourth vertical acceleration, and Aa1, Aa2 and Aa3 are thefirst to third vertical accelerations, respectively.

Referring to Equation 2, the fourth vertical acceleration Ad at theposition of the fourth damper where a vertical acceleration sensor isnot installed is obtained by multiplying the vertical accelerations Aa1,Aa2 and Aa3 measured in the first to third vertical acceleration sensors10, 12 and 14 by the corresponding correction constants α, β and γ andsubsequently summing up the first to third accelerations that have beenmultiplied by the correction constants.

At this time, the correction constants α, β and γ are obtained from thefollowing procedures.

For example, assuming that a plane equation P for the verticalacceleration sensors installed on the vehicle body is Z=AX+BY+C, all thecoordinate values of the respective vertical acceleration sensors areincluded in the equation P.(X1,Y1,Z1),(X2,Y2,Z2),(X3,Y3,Z3)∈P,  (3)where A, B and C are constants, which are expressed as the followingEquations 4 to 6, respectively. $\begin{matrix}{A = \frac{{\left( {Z_{1} - Z_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {Z_{1} - Z_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} & (4) \\{B = \frac{{\left( {X_{1} - X_{2}} \right)\left( {Z_{1} - Z_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Z_{1} - Z_{2}} \right)}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} & (5) \\\begin{matrix}{C = {{Z\quad 1} - {A\quad X\quad 1} - \quad{B\quad Y\quad 1}}} \\{= {{Z\quad 2} - {A\quad X\quad 2} - {B\quad Y\quad 2}}} \\{= {{Z\quad 3} - {A\quad X\quad 3} - {B\quad Y\quad 3}}}\end{matrix} & (6)\end{matrix}$

At this time, assuming that the installation positions of the threevertical acceleration sensors are upper points on the dampers and in acommon plane and Y coordinate values of the front first and secondvertical acceleration sensors are the same (i.e., Y₁=Y₂), the threevertical acceleration sensors output the accelerations of {umlaut over(z)}₁, {umlaut over (z)}₂ and {umlaut over (z)}₃, respectively.

The plane equation for the first to fourth dampers installed on thevehicle body is considered to be z=Ax+By+C, and is then subjected tosecond differentiation. At this time, the positions of the dampers areexpressed using x and y. $\begin{matrix}{\frac{\mathbb{d}{\,^{2}z}}{\mathbb{d}t^{2}} = {{\frac{\mathbb{d}{\,^{2}A}}{\mathbb{d}t^{2}}x} + {\frac{\mathbb{d}{\,^{2}B}}{\mathbb{d}t^{2}}y} + \frac{\mathbb{d}{\,^{2}C}}{\mathbb{d}t^{2}}}} & (7) \\{{{\frac{\mathbb{d}{\,^{2}A}}{\mathbb{d}t^{2}}\left( {Z_{1},Z_{2},Z_{3}} \right)} = {{\frac{\partial A}{\partial Z_{1}}{\overset{¨}{Z}}_{1}} + {\frac{\partial A}{\partial Z_{2}}{\overset{¨}{Z}}_{2}} + {\frac{\partial A}{\partial Z_{3}}{\overset{¨}{Z}}_{3}}}},{{{where}\quad\frac{\partial Z_{i}}{\partial t^{2}}} = {{\overset{¨}{Z}}_{i}.}}} & (8)\end{matrix}$

Since A is a function of Z1, Z2 and Z3 and Z1, Z2, and Z3 are alsofunctions of time, a derivative of A with respect to time is expressedas Equation 8 using a chain rule. Equation 8 can be expressed asEquation 9 by rearranging it according to the accelerations of therespective sensors after expanding Equation 8 with respect to respectivecoefficients. $\begin{matrix}\begin{matrix}{\frac{\mathbb{d}\quad{\,^{2}\quad z}}{\mathbb{d}\quad t^{\quad 2}} = {{\left( {{\frac{\partial A}{\partial Z_{1}}x} + {\frac{\partial B}{\partial Z_{1}}y} + \frac{\partial C}{\partial Z_{1}}} \right){\overset{¨}{Z}}_{1}} +}} \\{{\left( {{\frac{\partial A}{\partial Z_{2}}x} + {\frac{\partial B}{\partial Z_{2}}y} + \frac{\partial C}{\partial Z_{2}}} \right){\overset{¨}{Z}}_{2}} +} \\{\left( {{\frac{\partial A}{\partial Z_{3}}x} + {\frac{\partial B}{\partial Z_{3}}y} + \frac{\partial C}{\partial Z_{3}}} \right){\overset{¨}{Z}}_{3}}\end{matrix} & (9) \\{\frac{\mathbb{d}\quad{\,^{2}\quad z}}{\mathbb{d}\quad t^{\quad 2}} = {{{\alpha\left( {x,y} \right)}{\overset{¨}{Z}}_{1}} + {{\beta\left( {x,y} \right)}{\overset{¨}{Z}}_{2}} + {{\gamma\left( {x,y} \right)}{\overset{¨}{Z}}_{3}}}} & (10)\end{matrix}$

Thus, the correction constants α, β and γ at the damper positions (x, y)of the dampers are expressed as the following Equation 11.$\begin{matrix}{{{\alpha\left( {x,y} \right)} = {{\frac{\partial A}{\partial Z_{1}}x} + {\frac{\partial B}{\partial Z_{1}}y} + \frac{\partial C}{\partial Z_{1}}}}{{\beta\left( {x,y} \right)} = {{\frac{\partial A}{\partial Z_{2}}x} + {\frac{\partial B}{\partial Z_{2}}y} + \frac{\partial C}{\partial Z_{2}}}}{{\gamma\left( {x,y} \right)} = {{\frac{\partial A}{\partial Z_{3}}x} + {\frac{\partial B}{\partial Z_{3}}y} + \frac{\partial C}{\partial Z_{3}}}}{\frac{\partial A}{\partial Z_{1}},{\frac{\partial A}{\partial Z_{2}}\quad{and}\quad\frac{\partial A}{\partial Z_{3}}}}} & (11)\end{matrix}$existing in Equation 9 and the correction constants α, β and γ can beobtained as the following Equation 12. $\begin{matrix}{{\frac{\partial A}{\partial Z_{1}} = \frac{Y_{2} - Y_{3}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}{\frac{\partial A}{\partial Z_{2}} = \frac{Y_{3} - Y_{1}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}{\frac{\partial A}{\partial Z_{3}} = \frac{Y_{1} - Y_{2}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}} & (12)\end{matrix}$

Further,$\frac{\partial B}{\partial Z_{1}},{\frac{\partial B}{\partial Z_{2}}\quad{and}\quad\frac{\partial B}{\partial Z_{3}}}$existing in Equation 9 and the correction constants α, β and γ can beobtained as the following Equation 13. $\begin{matrix}{{\frac{\partial B}{\partial Z_{1}} = \frac{X_{3} - X_{2}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}{\frac{\partial B}{\partial Z_{2}} = \frac{X_{1} - X_{3}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}{\frac{\partial B}{\partial Z_{3}} = \frac{X_{2} - X_{1}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}} & (13)\end{matrix}$

Furthermore,$\frac{\partial C}{\partial Z_{1}},{\frac{\partial C}{\partial Z_{2}}\quad{and}\quad\frac{\partial C}{\partial Z_{3}}}$existing in Equation 9 and the correction constants α, β and γ can beobtained as the following Equation 14. $\begin{matrix}{{\frac{\partial C}{\partial Z_{1}} = {{1 - {\frac{\partial A}{\partial Z_{1}}X_{1}} - {\frac{\partial B}{\partial Z_{1}}Y_{1}}} = \frac{{X_{2}Y_{3}} - {X_{3}Y_{2}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}}{\frac{\partial C}{\partial Z_{2}} = {{1 - {\frac{\partial A}{\partial Z_{2}}X_{2}} - {\frac{\partial B}{\partial Z_{2}}Y_{2}}} = \frac{{X_{3}Y_{1}} - {X_{1}Y_{3}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}}{\frac{\partial C}{\partial Z_{3}} = {{1 - {\frac{\partial A}{\partial Z_{3}}X_{3}} - {\frac{\partial B}{\partial Z_{3}}Y_{3}}} = \frac{{X_{1}Y_{2}} - {X_{2}Y_{1}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}}} & (14)\end{matrix}$

When the values obtained from Equations 12 to 14 are substituted intoEquation 11, the correction constants α, β and γ at the position (x, y)of the fourth damper where a vertical acceleration sensor is notinstalled can be obtained as Equation 15 from the position coordinatevalues (X₁, X₂, X₃) and (Y₁, Y₂, Y₃) of the three vertical accelerationsensors 10, 12 and 14. $\begin{matrix}\begin{matrix}{{\alpha\left( {x,y} \right)} = \frac{{\left( {Y_{2} - Y_{3}} \right)x} + {\left( {X_{3} - X_{2}} \right)y} + {X_{2}Y_{3}} - {X_{3}Y_{2}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{{\beta\left( {x,y} \right)} = \frac{{\left( {Y_{3} - Y_{1}} \right)x} + {\left( {X_{1} - X_{3}} \right)y} + {X_{3}Y_{1}} - {X_{1}Y_{3}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{{\gamma\left( {x,y} \right)} = \frac{{\left( {Y_{1} - Y_{2}} \right)x} + {\left( {X_{2} - X_{1}} \right)y} + {X_{1}Y_{2}} - {X_{2}Y_{1}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}\end{matrix} & (15)\end{matrix}$

When the correction constants α, β and γ obtained from Equation 15 andthe vertical accelerations Aa1, Aa2 and Aa3 of the first to thirdvertical acceleration sensors 10, 12 and 14 are substituted intoEquation 2, the ECU 16 can obtain the vertical acceleration Ad at theposition of the fourth damper 24 in which a vertical acceleration sensoris not installed.

Further, the ECU 16 of the present invention corrects the verticalaccelerations of the first to third vertical acceleration sensors 10, 12and 14 to the vertical accelerations at the positions of the first tothird dampers 18, 20 and 22 using the following Equation 16.Aα _(n)[1]=α[1]×Aα[1]+β[1]×Aα[2]+β[1]×Aα[3]Aα _(n)[2]=α[2]×Aα[1]+β[2]×Aα[2]+β[2]×Aα[3]Aα _(n)[3]=α[3]×Aα[1]+β[3]×Aα[2]+β[3]×Aα[3],  (16)where Aa_(n)[1], Aa_(n)[2] and Aa_(n)[3] are values corrected to thevertical accelerations at the positions of the first to third dampers.α[1], β[1] and γ[1] are correction constants at the position of thefirst damper, α[2], β[2] and γ[2] are correction constants at theposition of the second damper, and α[3], β[3] and γ[3] are correctionconstants at the position of the third damper.

For example, as shown in Table 1 below, if the X and Y positioncoordinate values of the first to third vertical acceleration sensorsare given (1500, 1800), (200, 1800) and (1400, 300) and the x and yposition coordinate values of the first to fourth dampers are given(1700, 2000), (0, 2000), (1600, 500) and (100, 500), respectively, thecorrection constants α, β and γ at the positions of the respectivedampers are obtained. Then, from the correction constants at theposition of the fourth damper and the X and Y position coordinate valuesof the first to third vertical acceleration sensors, the fourth verticalacceleration, i.e., the vertical acceleration at the position of thefourth damper can be obtained, which is not shown in Table 1. TABLE 11^(st) 2^(nd) 3^(rd) 4^(th) Vertical Vertical Vertical VerticalAccelera- Accelera- Accelera- Accelera- tion Sensor tion Sensor tionSensor tion Vertical X 1500 200 1400 Accelera- Y 1800 1800 300 tionSensor Damper x 1700 0 1600 100 y 2000 2000 500 500 α 0.405 0.030 0.2760.876 β 2.471 2.292 −0.143 1.164 γ −0.133 −0.133 0.866 0.866

The ECU 16 of the present invention outputs signals for controlling thedamping forces of the first to fourth dampers 18, 20, 22 and 24 in orderto improve the ride comfort of the vehicle according to the valuescorrected to the vertical accelerations at the positions of the first tofourth dampers using the correction constants α, β and γ at thepositions of the respective dampers. Thus, the first to fourth actuators26, 28, 30 and 32 are operated with the damping forces.

FIG. 3 is a view showing the positions of the four dampers and threevelocity sensors of the vehicle employing the semi-active suspensionsystem. Referring to FIG. 3, two velocity sensors 100 and 102 aremounted adjacent to the front dampers 18 and 20 of the vehicle body 1,respectively, while a velocity sensor 104 is mounted adjacent to one ofthe rear dampers 22 and 24. Here, when “X” designates the widthdirection of the vehicle body and “Y” designates the longitudinaldirection thereof, the positions of the two front velocity sensors 100and 102 are (X₂, Y₂) and (X₁, Y₁), respectively, and the position of therear velocity sensor 104 is (X₃, Y₃). Since unexplained referencenumerals are the same as those shown in FIG. 1, descriptions thereofwill be omitted.

In the present invention, correction constants for a velocity at aposition where a fourth velocity sensor would be installed are obtainedusing the X and Y position coordinate values (for example, X₁-X₂ andY₁-Y₃) among the three velocity sensors 100, 102 and 104.

FIG. 4 is a block diagram of the semi-active suspension system,illustrating a method for measuring a velocity according to the presentinvention. Referring to this figure, the semi-active suspension systemcomprises the first to third velocity sensors 100, 102 and 104, the ECU16, the first to fourth dampers 18, 20, 22 and 24, and the first tofourth actuators 26, 28, 30 and 32. Here, the first to third velocitysensors 100, 102 and 104 are sensors installed adjacent to three of thefour dampers on the vehicle body so as to measure the velocity of thevehicle.

In the semi-active suspension system configured as above, the method formeasuring the velocity according to the present invention is performedas follows. Meanwhile, since a velocity is obtained by integrating anacceleration in the method for measuring the velocity of the presentinvention, the same equations as those described in the aforementionedmethod for measuring the acceleration will be used.

First, velocities Va1, Va2 and Va3 measured by the respective first tothird velocity sensors 100, 102 and 104 are input into the ECU 16.

The ECU 16 receives the velocities Va1, Va2 and Va3 measured by therespective first to third velocity sensors 100, 102 and 104 and obtainsa fourth velocity Vd using Equation 17 as follows:Vd=α×Vα1+β×Vα2+γ×Vα3,  (17)where α, β and γ are correction constants for the position of the fourthdamper where a fourth velocity sensor is not installed , Vd is thefourth velocity, and Va1, Va2 and Va3 are the first to third velocities,respectively.

Referring to Equation 17, the fourth velocity Vd at the position of thefourth damper where a velocity sensor is not installed is obtained bymultiplying the vertical velocities Va1, Va2 and Va3 measured in thefirst to third velocity sensors 100, 102 and 104 by the correspondingcorrection constants α, β and γ and subsequently summing up the first tothird velocities that have been multiplied by the correction constants.

The correction constants α, β and γ by which the respective velocitiesare multiplied are obtained as follows.

For example, assuming that a plane equation P for the velocity sensorsinstalled on the vehicle body is Z=AX+BY+C, all the coordinate values ofthe respective velocity sensors are included in the equation P.(X1,Y1,Z1),(X2,Y2,Z2),(X3,Y3,Z3)∈P,  (18)where A, B and C are constants, which are expressed as the followingEquations 19 to 21, respectively. $\begin{matrix}{A = \frac{{\left( {Z_{1} - Z_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {Z_{1} - Z_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} & (19) \\{B = \frac{{\left( {X_{1} - X_{2}} \right)\left( {Z_{1} - Z_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Z_{1} - Z_{2}} \right)}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} & (20) \\\begin{matrix}{C = {{Z\quad 1} - {A\quad X\quad 1} - {B\quad Y\quad 1}}} \\{= {{Z\quad 2} - {A\quad X\quad 2} - {B\quad Y\quad 2}}} \\{= {{Z\quad 3} - {A\quad X\quad 3} - {B\quad Y\quad 3}}}\end{matrix} & (21)\end{matrix}$

At this time, assuming that the installation positions of the threevelocity sensors are upper points on the dampers and in a common plane,and Y coordinate values of the front first and second velocity sensorsare the same (i.e., Y₁=Y₂), the three velocity sensors output thevelocities of {dot over (Z)}₁, {dot over (Z)}₂ and {dot over (Z)}₃,respectively.

The plane equation for the first to fourth dampers installed on thevehicle body is considered to be z=Ax+By+C, and is then subjected tofirst differentiation. At this time, the positions of the dampers areexpressed using x and y. $\begin{matrix}{\frac{\mathbb{d}z}{\mathbb{d}t} = {{\frac{\mathbb{d}A}{\mathbb{d}t}x} + {\frac{\mathbb{d}B}{\mathbb{d}t}y} + \frac{\mathbb{d}C}{\mathbb{d}t}}} & (22) \\{{{\frac{\mathbb{d}A}{\mathbb{d}t}\left( {Z_{1},Z_{2},Z_{3}} \right)} = {\frac{\partial A}{\partial Z_{1}}{\overset{.}{Z}}_{1}\frac{\partial A}{\partial Z_{2}}{\overset{.}{Z}}_{2}\frac{\partial A}{\partial Z_{3}}{\overset{.}{Z}}_{3}}},{{{where}\quad\frac{\partial Z_{i}}{\partial t}} = {{\overset{.}{Z}}_{i}.}}} & (23)\end{matrix}$

Since A is a function of Z1, Z2 and Z3 and Z1, Z2, and Z3 are alsofunctions of time, a derivative of A with respect to time is expressedas Equation 23 using a chain rule. That is, Equation 23 can be expressedas Equation 24 by rearranging it according to the velocities of therespective sensors after expanding Equation 23 with respect torespective coefficients. $\begin{matrix}\begin{matrix}{\frac{\mathbb{d}z}{\mathbb{d}t} = {{\left( {{\frac{\partial A}{\partial\quad Z_{\quad 1}}x} + {\frac{\partial B}{\partial\quad Z_{\quad 1}}y} + \frac{\partial C}{\partial\quad Z_{\quad 1}}} \right){\overset{.}{Z}}_{\quad 1}} +}} \\{{\left( {{\frac{\partial A}{\partial\quad Z_{\quad 2}}x} + {\frac{\partial B}{\partial\quad Z_{\quad 2}}y} + \frac{\partial C}{\partial\quad Z_{\quad 2}}} \right){\overset{.}{Z}}_{\quad 2}} +} \\{\left( {{\frac{\partial A}{\partial\quad Z_{\quad 3}}x} + {\frac{\partial A}{\partial\quad Z_{\quad 3}}y} + \frac{\partial A}{\partial\quad Z_{\quad 3}}} \right){\overset{.}{Z}}_{\quad 3}}\end{matrix} & (24) \\{\frac{\mathbb{d}z}{\mathbb{d}t} = {{{\alpha\left( {x,y} \right)}{\overset{.}{Z}}_{1}} + {{\beta\left( {x,y} \right)}{\overset{.}{Z}}_{2}} + {{\gamma\left( {x,y} \right)}{\overset{.}{Z}}_{3}}}} & (25)\end{matrix}$

Thus, the correction constants α, β and γ at the damper positions (x, y)of the dampers are expressed as the following Equation 26.$\begin{matrix}{\begin{matrix}{{\alpha\left( {x,y} \right)} = {{\frac{\partial A}{\partial Z_{1}}x} + {\frac{\partial B}{\partial Z_{1}}y} + \frac{\partial C}{\partial Z_{1}}}} \\{{\beta\left( {x,y} \right)} = {{\frac{\partial A}{\partial Z_{2}}x} + {\frac{\partial B}{\partial Z_{2}}y} + \frac{\partial C}{\partial Z_{2}}}} \\{{\gamma\left( {x,y} \right)} = {{\frac{\partial A}{\partial Z_{3}}x} + {\frac{\partial B}{\partial Z_{3}}y} + \frac{\partial C}{\partial Z_{3}}}}\end{matrix}{\frac{\partial A}{\partial Z_{1}},{\frac{\partial A}{\partial Z_{2}}\quad{and}\quad\frac{\partial A}{\partial Z_{3}}}}} & (26)\end{matrix}$existing in Equation 26 and the correction constants α, β and γ can beobtained as the following Equation 27. $\begin{matrix}\begin{matrix}{\frac{\partial A}{\partial Z_{1}} = \frac{Y_{2} - Y_{3}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{\frac{\partial A}{\partial Z_{2}} = \frac{Y_{3} - Y_{1}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{\frac{\partial A}{\partial Z_{3}} = \frac{Y_{1} - Y_{2}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}\end{matrix} & (27)\end{matrix}$

Further,$\frac{\partial B}{\partial Z_{1}},{\frac{\partial B}{\partial Z_{2}}\quad{and}\quad\frac{\partial B}{\partial Z_{3}}}$existing in Equation 26 and the correction constants α, β and γ can beobtained as the following Equation 28. $\begin{matrix}\begin{matrix}{\frac{\partial B}{\partial Z_{1}} = \frac{X_{3} - X_{2}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{\frac{\partial B}{\partial Z_{2}} = \frac{X_{1} - X_{3}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{\frac{\partial B}{\partial Z_{3}} = \frac{X_{2} - X_{1}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}\end{matrix} & (28)\end{matrix}$

Furthermore,$\frac{\partial C}{\partial Z_{1}},{\frac{\partial C}{\partial Z_{2}}\quad{and}\quad\frac{\partial C}{\partial Z_{3}}}$existing in Equation 26 and the correction constants α, β and γ can beobtained as the following Equation 29. $\begin{matrix}\begin{matrix}{\frac{\partial C}{\partial Z_{1}} = {1 - {\frac{\partial A}{\partial Z_{1}}X_{1}} - {\frac{\partial B}{\partial Z_{1}}Y_{1}}}} \\{= \frac{{X_{2}Y_{3}} - {X_{3}Y_{2}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{\frac{\partial C}{\partial Z_{2}} = {1 - {\frac{\partial A}{\partial Z_{2}}X_{2}} - {\frac{\partial B}{\partial Z_{2}}Y_{2}}}} \\{= \frac{{X_{3}Y_{1}} - {X_{1}Y_{3}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}} \\{\frac{\partial C}{\partial Z_{3}} = {1 - {\frac{\partial A}{\partial Z_{3}}X_{3}} - {\frac{\partial B}{\partial Z_{3}}Y_{3}}}} \\{= \frac{{X_{1}Y_{2}} - {X_{2}Y_{1}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}\end{matrix} & (29)\end{matrix}$

When the values obtained from Equations 27 to 29 are substituted intoEquation 26, the correction constants α, β and γ at the position (x, y)of the fourth damper where a velocity sensor is not installed can beobtained as Equation 30 from the position coordinate values (X₁, X₂, X₃)and (Y₁, Y₂, Y₃) of the three velocity sensors 100, 102 and 104.$\begin{matrix}{{{\alpha\left( {x,y} \right)} = \frac{{\left( {Y_{2} - Y_{3}} \right)x} + {\left( {X_{3} - X_{2}} \right)y} + {X_{2}Y_{3}} - {X_{3}Y_{2}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}{{\beta\left( {x,y} \right)} = \frac{{\left( {Y_{3} - Y_{1}} \right)x} + {\left( {X_{1} - X_{3}} \right)y} + {X_{3}Y_{1}} - {X_{1}Y_{3}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}{{\gamma\left( {x,y} \right)} = \frac{{\left( {Y_{1} - Y_{2}} \right)x} + {\left( {X_{2} - X_{1}} \right)y} + {X_{1}Y_{2}} - {X_{2}Y_{1}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}}} & (30)\end{matrix}$

When the correction constants α, β and γ obtained from Equation 30 andthe velocities Va1, Va2 and Va3 of the first to third velocity sensors100, 102 and 104 are substituted into Equation 17, the ECU 16 can obtainthe velocity Vd at the position of the fourth damper 24 where a velocitysensor is not installed.

Further, the ECU 16 of the present invention corrects the velocities ofthe first to third velocity sensors 100, 102 and 104 to the velocitiesat the positions of the first to third dampers 18, 20 and 22 using thefollowing Equation 31.Vα _(n)[1]=α[1]×Vα[1]+β[1]×Vα[2]+β[1]×Vα[3]Vα _(n)[2]=α[2]×Vα[1]+β[2]×Vα[2]+β[2]×Vα[3]Vα _(n)[3]=α[3]×Vα[1]+β[3]×Vα[2]+β[3]×Vα[3],  (31)where Va_(n)[1], Va_(n)[2] and Va_(n)[3] are values corrected to thevelocities at the positions of the first to third dampers. α[1], β[1]and γ[1] are correction constants at the position of the first damper,α[2], β[2] and γ[2] are correction constants at the position of thesecond damper, and α[3], β[3] and γ[3] are correction constants at theposition of the third damper.

Therefore, when the X and Y position coordinate values of the first tothird velocity sensors and the x and y position coordinate values of thefirst to fourth dampers are given, the correction constants α, β and γat the positions of the respective dampers are. obtained in the ECU 16of the present invention. Then, from the correction constants at theposition of the fourth damper and the X and Y position coordinate valuesof the first to third velocity sensors, the fourth velocity, i.e., thevelocity at the position of the fourth damper, can be obtained. Further,signals for controlling the damping forces of the first to fourthdampers 18, 20, 22 and 24 are output in order to improve the ridecomfort of the vehicle according to the values corrected to thevelocities at the positions of the first to fourth dampers. Thus, thefirst to fourth actuators 26, 28, 30 and 32 are operated with thecontrolled damping forces.

As described above, according to the present invention, the fourthvertical acceleration can be obtained by multiplying the three verticalaccelerations measured from the three acceleration sensors by theconstants for correcting them to accelerations at actually desireddamper positions and subsequently summing up them. Then, by multiplyingthe vertical accelerations measured from the three acceleration sensorsby the correction constants at the corresponding damper positions, thecorrected vertical accelerations can be obtained.

Thus, according to the present invention, vertical accelerations at thepositions of the dampers can be obtained and the vertical accelerationsmeasured from the sensors can be corrected using the correctionconstants, so that there is an advantage in that the ride comfort of avehicle can be more correctly controlled using the corrected verticalaccelerations.

In addition, the present invention can be applied to velocity sensorsinstead of vertical acceleration sensors so as to more correctly controlthe ride comfort of a vehicle.

The present invention is not limited to the embodiments described abovebut may be modified or changed in various manners by those skilled inthe art within the scope and the technical spirit of the inventiondefined by the appended claims.

1. A method for obtaining a vertical acceleration from verticalaccelerations measured from three vertical acceleration sensors of asemi-active suspension system of a vehicle, comprising the steps of:receiving first to third vertical accelerations measured from first tothird vertical acceleration sensors; and obtaining a fourth verticalacceleration (Ad) by multiplying the first to third verticalaccelerations by correction constants and subsequently summing up them,according to the following equation:Ad=α ^(x) Aα1+β^(x) Aα2+γ^(x) Aα3, where α, β and γ are the correctionconstants at the position of a damper where a vertical accelerationsensor is not installed, Ad is the fourth vertical acceleration, andAa1, Aa2 and Aa3 are the first to third vertical accelerations,respectively.
 2. The method as claimed in claim 1, wherein thecorrection constants α, β and γ are obtained from the followingequations using X and Y position coordinate values of the first to thirdvertical acceleration sensors and x and y position coordinate values ofthe damper where a vertical acceleration sensor is not installed:${\alpha\left( {x,y} \right)} = \frac{{\left( {Y_{2} - Y_{3}} \right)x} + {\left( {X_{3} - X_{2}} \right)y} + {X_{2}Y_{3}} - {X_{3}Y_{2}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}$${\beta\left( {x,y} \right)} = \frac{{\left( {Y_{3} - Y_{1}} \right)x} + {\left( {X_{1} - X_{3}} \right)y} + {X_{3}Y_{1}} - {X_{1}Y_{3}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}$${{\gamma\left( {x,y} \right)} = \frac{{\left( {Y_{1} - Y_{2}} \right)x} + {\left( {X_{2} - X_{1}} \right)y} + {X_{1}Y_{2}} - {X_{2}Y_{1}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}},$where X₁, X₂ and X₃ are X position coordinate values of the first tothird vertical acceleration sensors, Y₁, Y₂ and Y₃ are Y positioncoordinate values of the first to third vertical acceleration sensors,and x and y are X and Y position coordinate values of the damper where avertical acceleration sensor is not installed.
 3. The method as claimedin claim 1 or 2, after the step of obtaining the fourth verticalacceleration, further comprising the step of correcting the first tothird vertical accelerations measured from the vertical accelerationsensors to vertical accelerations at the positions of correspondingdampers using the following equations:Aα _(n)[1]=α[1]×Aα[1]+β[1]×Aα[2]+β[1]×Aα[3]Aα _(n)[2]=α[2]×Aα[1]+β[2]×Aα[2]+β[2]×Aα[3]Aα _(n)[3]=α[3]×Aα[1]+β[3]×Aα[2]+β[3]×Aα[3], where Aa_(n)[1], Aa_(n)[2]and Aa_(n)[3] are values corrected to the vertical accelerations at thepositions of first to third dampers, α [1], β [1] and γ [1] arecorrection constants at the position of the first damper, α [2], β [2]and γ [2] are correction constants at the position of the second damper,and α [3], β [3] and γ [3] are correction constants at the position ofthe third damper.
 4. A method for obtaining a velocity from velocitiesmeasured from three velocity sensors of a semi-active suspension systemof a vehicle, comprising the steps of: receiving first to thirdvelocities measured from first to third velocity sensors; and obtaininga fourth velocity (Vd) by multiplying the first to third velocities bycorrection constants and subsequently summing up them, according to thefollowing equation:Vd=α ^(x) Vα1+β^(x) Vα2+γ^(x) Vα3, where α, β and γ are the correctionconstants at the position of a damper where a velocity sensor is notinstalled, Vd is the fourth velocity, and Va1, Va2 and Va3 are the firstto third velocities, respectively.
 5. The method as claimed in claim 4,wherein the correction constants α, β and γ are obtained from thefollowing equations using X and Y position coordinate values of thefirst to third velocity sensors and x and y position coordinate valuesof the damper where a vertical acceleration sensor is not installed:${\alpha\left( {x,y} \right)} = \frac{{\left( {Y_{2} - Y_{3}} \right)x} + {\left( {X_{3} - X_{2}} \right)y} + {X_{2}Y_{3}} - {X_{3}Y_{2}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}$${\beta\left( {x,y} \right)} = \frac{{\left( {Y_{3} - Y_{1}} \right)x} + {\left( {X_{1} - X_{3}} \right)y} + {X_{3}Y_{1}} - {X_{1}Y_{3}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}$${{\gamma\left( {x,y} \right)} = \frac{{\left( {Y_{1} - Y_{2}} \right)x} + {\left( {X_{2} - X_{1}} \right)y} + {X_{1}Y_{2}} - {X_{2}Y_{1}}}{{\left( {X_{1} - X_{2}} \right)\left( {Y_{1} - Y_{3}} \right)} - {\left( {X_{1} - X_{3}} \right)\left( {Y_{1} - Y_{2}} \right)}}},$where X₁, X₂ and X₃ are X position coordinate values of the first tothird velocity sensors, Y₁, Y₂ and Y₃ are Y position coordinate valuesof the first to third velocity sensors, and x and y are X and Y positioncoordinate values of the damper where a vertical acceleration sensor isnot installed.
 6. The method as claimed in claim 4 or 5, after the stepof obtaining the fourth velocity, further comprising the step ofcorrecting the first to third velocities measured from the velocitysensors to velocities at the positions of corresponding dampers usingthe following equations:Vα _(n)[1]=α[1]×Vα[1]+β[1]×Vα[2]+β[1]×Vα[3]Vα _(n)[2]=α[2]×Vα[1]+β[2]×Vα[2]+β[2]×Vα[3]Vα _(n)[3]=α[3]×Vα[1]+β[3]×Vα[2]+β[3]×Vα[3], where Va_(n)[1], Va_(n)[2]and Va_(n)[3] are values corrected to the velocities at the positions offirst to third dampers, α [1], β [1] and γ [1] are correction constantsat the position of the first damper, α [2], β [2] and γ [2] arecorrection constants at the position of the second damper, and α [3], β[3] and γ [3] are correction constants at the position of the thirddamper.